Background Harsh environments are known to predict deficits in children's cognitive abilities. Life history theory approaches challenge this interpretation, proposing stressed children's cognition becomes specialized to solve problems in fitness‐enhancing ways. The goal of this study was to examine associations between early environmental harshness and children's problem‐solving outcomes across tasks varying in ecological relevance. In addition, we utilize an evolutionary model of temperament toward further specifying whether hawk temperament traits moderate these associations. Methods Two hundred and one mother–child dyads participated in a prospective multimethod study when children were 2 and 4 years old. At age 2, environmental harshness was assessed via maternal report of earned income and observations of maternal disengagement during a parent–child interaction task. Children's hawk temperament traits were assessed from a series of unfamiliar episodes. At age 4, children's reward‐oriented and visual problem‐solving were measured. Results Path analyses revealed early environmental harshness and children's hawk temperament traits predicted worse visual problem‐solving. Results showed a significant two‐way interaction between children's hawk temperament traits and environmental harshness on reward‐oriented problem‐solving. Simple slope analyses revealed the effect of environmental harshness on reward‐oriented problem‐solving was specific to children with higher levels of hawk traits. Conclusions Results suggest early experiences of environmental harshness and child hawk temperament traits shape children's trajectories of problem‐solving in an environment‐fitting manner.